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But this increased opportunity to socialise and communicate in a virtual environment has offered new avenues for antisocial behaviour.

The problem of cyberbullying has received considerable research attention. However, other online antisocial behaviours with similarly harmful outcomes have received far less consideration - one example being anonymous online trolling.

Trolling behaviours typically include deliberately posting inflammatory comments and argumentative messages in an attempt to provoke, disrupt and upset others. "Trolls" may pretend to be part of the group, but their real intent is to create conflict for their own amusement. Shockingly, more than a quarter of Americans have admitted to engaging in trolling behaviour at some point.

Most concerning, however, is that harassing behaviours online (such as cyberbullying and trolling) are shown to have psychological outcomes similar to those of harassment offline. These outcomes can include depression, social anxiety and low self-esteem.

But while cyberbullying is a clear extension of offline bullying, there is no obvious real-world counterpart to online trolling. This can make it harder to grasp exactly why it happens.

Who are the trolls?

Research has defined a typical troll as an internet user who takes on a fake identity, which they then use to cause disruption and trigger conflict among others for their own amusement.

The cover of anonymity allows the troll to treat the internet as their personal playground, throwing provocative comments into forums like grenades into a crowd. Trolls remain unknown to victims and, unlike cyberbullying, their victims are unknown to them.

But trolling has largely eluded most attempts to control it - as shown by the huge numbers of people who admit to having done it.

Is there a trolling 'type'?

One way to try to understand why people engage in trolling is to investigate whether they are likely to show particular personality traits, such as narcissism, psychopathy, Machiavellianism and everyday sadism - known as the "dark tetrad".

These traits commonly underpin many forms of social manipulation and deception, and involve a drive for ruthless self-advancement, aggression and, most notably, a lack of empathy and severe callousness. Taking each of the tetrad in turn, narcissism is associated with feelings of superiority and ego-inflation; psychopathy is linked to impulsivity and callousness; Machiavellianism is associated with manipulation and exploitation of others; and sadism is defined as the enjoyment of inflicting pain on others.

A 2014 study found that people with higher levels of sadism, psychopathy and Machiavellianism were more likely to engage in online trolling behaviour, with sadism being the strongest predictor.

What's the ultimate motivation?

But research on trolling behaviours has not yet considered the direct motivating factors. So my recent research sought to understand what motivates individuals to engage in trolling behaviours.

If a behaviour is rewarding, an individual is more likely to do it. Because trolling depends on interaction with others, we were interested in the social rewards experienced by those who provoke these interactions.

Typical social rewards generally occur through reciprocal social behaviours and interactions. We experience positive (or typical) social rewards when we engage in helpful, altruistic behaviour. But in our study we explored atypical social rewards, also known as "negative social potency".

Negative social potency is measured using the Social Rewards Questionnaire, in which participants indicate their agreement with statements such as "I enjoy making someone angry" and "I enjoy embarrassing others".

These are the rewarding feelings that some people experience when creating social discord, through selfish or self-serving behaviours and interactions. Individuals who seek negative social potency are likely to enjoy inflicting psychological pain and distress on others.

They may achieve this through exerting negative social influence, power and strength.

Personality vs motivation

We gathered a sample of 396 adults (75.9% women and 24.10% men) and asked them to complete a questionnaire to measure their levels of narcissism, psychopathy, Machiavellianism and sadism.

We also assessed their orientation towards negative social potency and their engagement in trolling behaviours on Facebook.

Higher levels of psychopathy and sadism tend to predict trolling behaviours, with sadism being the strongest factor. We also found that men were more likely than women to engage in Facebook trolling.

But more surprising was what we found when we included negative social potency in the model. The effect of negative social potency was far stronger than the effects of psychopathy and sadism.

This means that while antisocial personality traits do play a role, what really influences trolling behaviour is the social pleasure derived from knowing that others are annoyed by it. The more negative social impact the troll has, the more their behaviour is reinforced.

Fighting back

Happily, this discovery suggests an easy way to deal with trolls: ignore them, rather than giving them the satisfaction of an angry reaction.

Individuals seeking a negative social reward may still engage in trolling. But if they don't receive that negative social reward, then their motivation to engage in this behaviour will likely diminish.

So it appears that the classic internet adage really does hold true: don't feed the trolls. Deny them the pleasure of an angry reaction, and they'll probably leave you alone.